This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. ATPRP3 (one member of a family extracellular matrix proteins) is exclusively expressed in growing root hairs and becomes cross-linked within the cell wall as growth ceases. We have shown that an atprp3-1 null mutant displays a complex phenotype including short branched root hairs, smaller roots and leaves, an earlier flowering time and a reduced ability to compete for resources when grown with wild type plants. All of these phenotypes are complemented when an epitope-tagged wild type copy of ATPRP3 is introduced into the mutant background. In order to identify key genes and pathways whose altered expression in root hairs contribute to the atprp3 phenotypes, we will use microarray analysis to compare gene expression in root hairs of wild type, the atprp3-1 mutant and a complemented atprp3-1mutant line. We expect to identify gene expression changes associated extracellular matrix synthesis as well as changes in gene expression of signaling pathways responsible for root hair metabolism and root/shoot communication. These observations will allow us to further investigate the mechanism through which extracellular matrix structure can affect cell shape and function in a tip-growing cell.